Wave guide variable attenuator



7 July 21, 1953 s. ROBERTS 2,646,551

WAVE GUIDE VARIABLE ATTENUATOR Filed Feb. 25. 1944 IN VEN TOR.

SHEPARD ROBER TS BY WM 94-11 XH- vrne of insulating material.

Patented July 21, 1953 V 7 2,646,551 J l Y WAVE cums v aIABLEnTTENUA'roRShepard Roberts, Cambridge, Mass, assignor, by

'mesneassignments, to the United 'States of- America as represented by'the Secretary of .War

nim iqeti n FebruaryZS, 1944, Serial ndszasss' fTClaims. (o1. sea-+3 1)@This invention relates to a guide control and particularly to avariable attenuator foruse in wave guides. v r

The principal object ofthe invention is to prof vide a simple,inexpensive and readily adjustable small strip dimension the maximumintensity electric vector.

Attenuation is btained by itioningthe sistance' stripwithin the guidespace so that the attenuator of this character whereinfthere is 1 littleor no reflection of the guided waves. I l ,I, In the accompanyingdrawing, Fig; 1 is a part.- ly cut-away perspective view of theinvention;

and Fig. 2 is a modification.

The attenuator is shown as embodied ma) rectangular metallic Wave guideportion 5, Fig. l,, which is constructed the. usual'mannerand with theusual ratio'of larger side to shorter. side and dimensions determined bytransmitted frequency. If desired, the attenuator may-"be applied to acircular wave guide having a mode of wave propagation where the maximumintensity electric vector lies in a diametral plane. An elongated stripof resistance material 6 is disposed within theguide portion, end 1 ofsaid strip being fixed to a shorter guide side by fastening means suchas bolt 8.

Thus the anchored end is at a region of said guide where the electricvector has its minimum intensity. Strip 6 may be comv posed of someinsulating material such as Bakelite with one side thereof coated with alayer of carbonaceous material to provide a desired resistancecharacteristic. The free end of the strip movable part, constitutesaneffect'ive portion" which may be moved from a position of-minimumelectric field intensity. (r'ight j up against the guide wall) to a'position of maximum field intensity (substantially in the center-of thespace provides visual indication of strip position, al-

is tapered as shown at 9, the longitudinal length of the taper being atleast a half wave length of the transmitted wave.

A micrometer or similar adjusting device I0 is fixed to the exterior ofthe waveguide portion and positioned in relation to the free end ofstrip 6. The guide portion is suitably apertured to received positioningpin ll of the micrometer.

enclosed-by the guide walls) The, micrometer though a simple screwcontrol or other means may be used'if desired.

The modification of Fig. z'shows an attenuator embodied in a rectangularwaveguide portion 20 constructed and dimensioned in the risualmanner. A-narrow centrallydisposedlongitudinal aperture 2| is provided in thelarger guide side. This aperture is along the line of intersection ofthe wave guide wall and plane of maximum electric field'intensity. Acircular guide may have a similar construction. The attenuator comprisesan elongated supporting metallic member 22, which is suitably connectedto the apertured guide side as by hinge 23. A thin sheet of resistancematerial 24 depends from supporting member 22 and registers withaperture 2|. The resistance sheet is wide at its central region andtapers or curves at least half a wave length to each end asshown. Thecenter width of sheet 24 substantially correspondsto the width of ashorter guide side so that the element may terminate just short of itsopposite guide side when moved 7 to its maximum position within theguide. Ele- This pin'bears on the surface of strip 6 near its free endand causes said strip to bend away from theguide side into the spacewithin the guide in accordance with micrometer adjustment. The pinispreferably of small diameter and may be A recovery spring 15 of mentsof hinge 23 may fit rather tightly so that friction will retain thepivoted attenuator in any predetermined position.

1 It'will be seen that the invention provides a readily variableattenuator for use with wave guides. .The device has been found to causelittle or no appreciable wave reflection. Having thus described theinvention, what I claim as new and desire to-secure by Letters Patentis: r

1. An attenuator for use. in a wave guide in which high frequencyelectric waves are progagated comprising a wave guide portion having a,

modeof propagation in which the maximumintensity electric vector lies ina fiat plane symmetrically through and longitudinal of said guideportion, a thin, fiat resistance member carried by said guide at aregion where the electric vector is substantially zero, and lyinggenerally in a plane parallel to that of the maximum intensity electricvector, and means for moving at least part of said member in a directiongenerally perpendicular to the maximum intensity electric is parallel tothe plane of 3 vector from a region of minimum field intensity to aregion of maximum field intensity.

2. The structure of claim 1 wherein said member has a tapered end alongthe line of wave propagation with the taper portion at least half a wavelength in the full attenuation position.

3. An attenuator for use in -agwave guide in which high frequencyelectric waves. are 'propagated comprising a wave guide portion having amode of propagation in which the maximum intensity electric vector liesin a flat plane sym v metrically through and longitudinal of said'guideportion, a thin, fiat resistance member mounted;

on said guide to lie in the maximum intensity" electric vector plane,said guide being: slottedttog clear said member and means for movingsaid. member from the exterior of meanders the irrterior thereof forvarying the attenuation; where a V in said member is pivotally mountedat one end thereof. with/the member having the general shape of asegment of a circle.

a 4, lncomhination, a hollow wave guide ri eali to vary the ntensity ofwaves transrr'li-tteditv r ethrough, said means. comprising aflexiblejdiele ctric, member attached to the inner wall or sai guide,and means arrangedexternally of said guide and connected withfsaidmemmer through a wall of said-guide variably. .to'adjustsaid'mem her inpositions extending from the'wall of said: guide toward the centerthereof graually along the lengthof a portion offthe guide, said dielectrie member carrying thereon resistance mate rial .to absorb the energyor said wave.

5. In combination, a dielectric wave guide along which a high'frequencywave s propagated comprising a hollow rectangular pipe having" walls ofconductive material and attenuating means for said wave comprising, athin strip of resistive material extending longitudinally along theinner surface of one of said walls, said strip having its endpresentedto a wave traveling gated strip having a conductive surface layer 'on atleast one'sidethereof with a resistance substantially. greater than thatof said guide surface,

said strip being positioned within said guide and extending lengthwisethereof with said side substan ally parallel tq the electric field ofsaid wer on said strip being secured to a wall of said guide with thestrip extending away from said point in angular relation to said wall.7'. In a high frequency system, a hollow tubular guideforan'electromagnetic wave, said guide having a conductive inner surface and arectangular transverse section with a pair of wide walls and ja pair'ofnarrow walls, and an elongated strip having a conductive surface layeron at i least one sidethereon with a resistance substantially greaterthan that of said guide surface, said strip being positionedwithin saidguide and extending lengthwise thereof with said side substanti-allyperpendiculartosaid "wide walls; a point onsaidstrip" beingsec'ured toone of said narrow walls with the strip extending away from said pointin angular relationv to said, one narrow wall. v v I p ROBERTS.References Cited in theme of this patent UNITED STATES; PATENTS

